Spark plug terminal



Aug- 14 1945- E. MosTHAF SPARK PLUG TERMINAL Filed April 20, 1943 I nven Lor 5D w//v MOSTHAF m y u V m agi orney Patented Aug. 14, 1945 UNITED STATES PATENT OFFICE 2 Claims.

My invention relates to improvements in spark plug cable terminals and more particularly those used on air-craft motors.

An object of my invention is to provide an inexpensive and durable vitrified spark plug terminal, which does not contract or expand, nor burn or char under the high temperature developed by the modern air-craft engine.

Another object of the invention is to provide easily a manufactured ceramic spark plug cable terminal resistant to groundings and ashovers.

Reference will be had to the accompanying drawing forming a part of this specification in which similar reference characters indicate corresponding parts throughout the several views.

Figure 1 is a sectional View of a spark plug with the terminal and cable in place.

Figure 2 is a sectional view of the ceramic tube before receiving the web.

Figure 3 is a sectional view of the ceramic tube with the web.

Figure 4 illustrates the spring which is affixed to the web.

Figure 5 illustrates in section the rivet used to affix the spring to the web.

Figure 6 is a sectional View of the terminal in its complete form.

The ceramic tube I found best fitted for this device is made from Steatite, a composition of commercial talc, a binder and water. The tube is extruded from the extrusion machine with proper inside and outside diameters in lengths many times the length of the cable terminal and dried by any accepted or practical method. This tube when extruded from the machine is larger in diameter than those required by the finished terminal to allow for shrinkage.

The tube extruded from the machine, after it has been dried, is cut into short pieces of sufficient length to allow for shrinkage. Each piece is slightly longer than the finished terminal. 'I'hese pieces are then kiln fired at a temperature which vitrifies the ceramic.

After the kiln firing the tube I0 is inspected for possible flaws or imperfections. It should have a smooth and glazed surface in and out so as to reduce to a minimum the possibility of flashovers or grounds caused by dirt sticking to the rough surface of the tube. A glazed surface does not attract dirt and can easily be wiped with a cloth.

To one end of the baked tube I0 is fitted a metal cup II. 'I'his cup has a hole I2 in its center, a flange I3 and a wall I4 defining the bowl portion of the cup. This metal cup is cemented into place by preferably using a paste made of borate of lead and water. 'I'he paste is coated around the wall I4, and the cup so coated, is then inserted in the tube with the flange I3 snug against the edge 0f the tube I0. The tube, cup and paste I5 is then heated to a temperature of approximately '700 degrees F., at which temperature the paste I5, between the wall I4 and the inner surface of the tube I0, fluxes into a hard glassy substance which binds the cup II and the tube I0 together.

After cooling, lthe spring I6 is attached to the cup II by means of rivet I1. This rivet is preferably made of malleable metal, is tubular in shape and is provided with a flange I8.

The tubular rivet I'I is first inserted in one end of the spring I 6 in a manner so that the flange I8 engages the first coil of the spring, then is inserted in the hole I2 of the cup II and riveted to the cup II with a setting punch.

Figure 6 better illustrates how the rivet is affixed to the cup and how the spring is held -between the cup and the flange I8 of the rivet I1. The terminal assembly is now ready for the electrical cable and the spark plug.

As illustrated in Figure 1 the tube I0 with the spring I6 affixed to it is inserted in the spark plug shell 20, the cable 2| having first been inserted in the tube I0, with the wire 2I skinned so as to protrude into the hole of the rivet I1 and so as to be in electrical contact with spring I8, which in turn is in electrical contact with the core 22 of the spark plug.

I am aware of the existence of ceramic terminals with an integral web near one end of the tube, but the manufacturing difficulties of such terminals are many and costly. To make a terminal with an integral web, in place of my metal cup, it is required that a rod be extruded from the extrusion machine with a comparatively small hole through the center. After this rod is dried it is cut to predetermined length. Then the small hole is enlarged by drilling four fifths of the entire length of the cut tube, then a recess is bored at the other end of the tube leaving a web between the long hole and the recess. This unit is then kiln-fired. The dimensions of all walls, lengths and web must .be very accurate, and must allow for a shrinkage of about 18%. Those skilled in the art realize the difficulties encountered in going through so many operations and so many dimensions, and a tolerance of ten thousandths of one inch for each and every part. A one or two thousandths of one inch difference in the inside or outside diameter, or in the depth of the leQess, or in the thickness of the web or rivet hole may render the entire unit unusable. Furthermore, many tubes crack, or become chipped when the spring is riveted to the web.

In my invention I extrude the tube with the proper outside and inside diameter allowing of course, for shrinkage. I cut the tube to proper lengths before flring it, and inspect only inner, outer walls and ends. By actual manufacturing tests of the two types it has been found that the self contained web type cost 3 times as much as mine. In my type there is very small rejection due to dimensional errors, and no cracking or chipping in riveting the spring to the metal cup.

Having described my invention I claim:

1. In a spark plug terminal, a ceramic insulating tube red to vitrication for receiving through one end a cable, a flanged metal cup inserted within the other end of said tube with the flange abutting the end face of said tube and glass-fired thereto and forming within the tube an insulated metallic wall having a web extending transversely within the tube,tand resilient contact .means secured to the metallic web and ex' tending axially of the tube adapted to contact the core terminal of a spark plug. thereby acting as a electrical conductor between a cable and the core terminal of a spark plug.

2. In a spark plug terminal, a ceramic insu`y lating tube ilred to vitriflcatlon and adapted to receive a cable through one of its ends, a metal cup fitted within the other end of the tube, said cup including a bowl portion having a transversely disposed apertured bottom and an outturned edge flange, the bowl portion of the cup being telescoped within the tube with the bottom of the cup extending transversely of the tube and with the under-face o1' said ange overlying and in contact with the end face of the tube, means for securing the cup within the tube including a' glass-Bred bond between the cup and tube, and a coil spring secured to the bottom of the cup and extending axially of the tube towards the adjacent end of the tube and adapted to contact the core terminal of a spark plug.

EDWIN MOSTHAF. 

